"pmcregs_in_use" flag is part of lppaca (Virtual Process Area),
which is used to indicate whether Performance Monitoring Unit (PMU) and
PMU sprs are in-use and whether should it be saved/restored by
hypervisor. ppc_set_pmu_inuse() is used to set/unset the VPA
flag "pmcregs_in_use". "pmcregs_in_use" flag is set in
"power_pmu_enable" via ppc_set_pmu_inuse(1) and it is unset
when there are no active events (n_events == 0 condition).
Patch here adds documentation on the ppc_set_pmu_inuse() usage.
Signed-off-by: Madhavan Srinivasan <ma...@linux.ibm.com>
Signed-off-by: Athira Rajeev <atraj...@linux.vnet.ibm.com>
---
arch/powerpc/perf/core-book3s.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 3086055..48bfdc9 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1285,6 +1285,11 @@ static void power_pmu_enable(struct pmu *pmu)
goto out;
if (cpuhw->n_events == 0) {
+ /*
+ * Indicate PMU not in-use to Hypervisor.
+ * We end-up here via "ctx_sched_out()" from common code and
+ * "power_pmu_del()".
+ */
ppc_set_pmu_inuse(0);
goto out;
}
@@ -1341,6 +1346,11 @@ static void power_pmu_enable(struct pmu *pmu)
* Write the new configuration to MMCR* with the freeze
* bit set and set the hardware events to their initial values.
* Then unfreeze the events.
+ * ppc_set_pmu_inuse(1): "power_pmu_enable" will unset the
+ * "pmcregs_in_use" flag when a previous profiling/sampling session
+ * is completed and un-setting of flag will notify the Hypervisor to
+ * drop save/restore of PMU sprs. Now that PMU need to be enabled, first
+ * set the "pmcregs_in_use" flag in VPA.
*/
ppc_set_pmu_inuse(1);
mtspr(SPRN_MMCRA, cpuhw->mmcr[2] & ~MMCRA_SAMPLE_ENABLE);
--
1.8.3.1
